Editing SOS (section)

{{Short description|International Morse code distress signal for help}}
{{Other uses}}
{{Listen|filename=SOS morse code.ogg|title=SOS|description=Audio of SOS in Morse code}}

'''SOS''' is a [[Morse code]] [[distress signal]] ({{morse|dot|dot|dot|dash|dash|dash|dot|dot|dot}}), used internationally, originally established for maritime use. In formal notation SOS is written with an overscore line ({{overbar|SOS}}), to indicate that the Morse code equivalents for the individual letters of "SOS" are transmitted as an unbroken sequence of three dots / three dashes / three dots, with no spaces between the letters.<ref>U.S. Navy, Bureau of Naval Personnel, [https://www.navy-radio.com/manuals/rm32-10228B-1957.pdf#page=149 ''Radioman 3 & 2''], NAVPERS 10228-B, Washington, D.C.: U.S.G.P.O., 1957, pp. 135, 177, 402.</ref> In [[Morse code#International Morse Code|International Morse Code]] three dots form the letter "S" and three dashes make the letter "O", so "S&nbsp;O&nbsp;S" became a common way to remember the order of the dots and dashes. IWB, VZE, 3B, and V7 form equivalent sequences, but traditionally SOS is the easiest to remember.

SOS, when it was first agreed upon by the [[International Radiotelegraph Convention (1906)|International Radio Telegraphic Convention]] in 1906, was merely a distinctive Morse code sequence and was initially not an abbreviation. Later a [[backronym]] was created for it in popular usage, and SOS became associated with mnemonic phrases such as "Save Our Souls" and "Save Our Ship".<ref>[https://babel.hathitrust.org/cgi/pt?id=hvd.ah6gfm&view=1up&seq=186 "S O S"], ''The Sailors' Magazine and Seaman's Friend'', October 1915, page 158.</ref> Moreover, due to its high-profile use in emergencies, the phrase "SOS" has entered general usage to informally indicate a crisis or the need for action.

[[File:Belgian road sign F62.svg|thumb|150px|The phrase "SOS" used on a Belgian [[emergency telephone]] traffic sign]]

SOS originated in [[German Empire|German government]] maritime radio regulations adopted effective 1&nbsp;April 1905. It became a worldwide standard when it was included in the service regulations of the first International Radiotelegraph Convention signed on 3&nbsp;November 1906, which became effective on 1&nbsp;July 1908. In modern terminology, SOS is a Morse "[[prosigns for Morse code|procedural signal]]" or "prosign{{-"}},<ref>{{cite book |last1=Weik |first1=Martin |title=Communications Standard Dictionary |date=2012 |publisher=Springer Science & Business Media |isbn=9781461304296 |page=760 |edition=3rd |url=https://books.google.com/books?id=pVvSBwAAQBAJ&pg=PA760}}</ref> used as a start-of-message mark for transmissions requesting assistance when loss of life or catastrophic loss of property is imminent.<ref>For emergency transmissions, SOS replaces CT = KA = '''{{morse|dash|dot|dash|dot|dash}}''', which is the marker for the start of routine messages.</ref> Other prefixes are used for mechanical breakdowns, requests for medical assistance, and a relayed distress signal originally sent by another station. SOS remained the maritime radio distress signal until 1999, when it was replaced by the [[Global Maritime Distress and Safety System]].<ref name="GMDSS Resolution">{{cite web |url=https://www.navcen.uscg.gov/pdf/marcomms/imo/Circulars/COM%20CIRC115.pdf |access-date=2019-08-18 |series=GMDSS Resolution |id=COM/Circ.115 |title=Discontinuation of Morse code services in the MF radiotelegraphy band |date=10 February 1993 |website=GMDSS |archive-date=2020-06-10 |archive-url=https://web.archive.org/web/20200610134908/https://www.navcen.uscg.gov/pdf/marcomms/imo/Circulars/COM%20CIRC115.pdf |url-status=dead }}</ref>

SOS is still recognized as a standard distress signal that may be used with any signaling method.<ref>U. S. Coast Guard, [https://www.navcen.uscg.gov/?pageName=NavRulesAmalgamated#Annex4 ''Amalgamated International and U. S. Inland Navigation Rules''], Annex IV, Retrieved October 24, 2018</ref> It has been used as a visual distress signal, consisting of three short/three long/three short flashes of light,<ref>{{Cite web|date=2021-04-15|title=How to Signal SOS With a Flashlight [Complete Guide]|url=https://lumenauthority.com/sos-signal-with-flashlight/|access-date=2021-07-07|website=Lumen Authority|language=en-US}}</ref> such as from a [[Mirror#Signalling|survival mirror]]. In some cases the individual letters "S&nbsp;O&nbsp;S" have been spelled out, for example, stamped in a snowbank or formed out of logs on a beach. "S&nbsp;O&nbsp;S" being readable upside down as well as right side up (as an [[ambigram]]) is an advantage for visual recognition.

[[File:SOS morse code from a flashlight.ogv|thumb|150px|SOS sent from a [[flashlight]]]]